Extrinsic and intrinsic influences on tree growth ? anatomical analysis of spruce branches

Abstract

In order to differentiate between environmental (extrinsic) influences affecting tree growth, and those causing (intrinsic) temporary irregularities in a single tree, we investigated the anatomy of three branches of comparable size and age, taken from two 60-year-old European spruces [Picea abies (L.) Karst]. Wood depositions in five consecutive internodes (4–8) along the branches were analysed. Internodal cross-sections were evaluated to discover whether extrinsic factors may have influenced the structure of the cambial xylogenic derivatives, or whether structural variations were caused by intrinsic events. Features occurring in all three branches were evaluated as extrinsically influenced. Observations like earlywood disturbances, distribution of resin ducts, duplication of radial files, and increments with narrow or broad latewood bands were considered. The ratio of radial cell number to ring width was used to define the vigour of cambial growth during the years covered. Meteorological data of the growing periods (May–September 1981–1988) representing mean values of temperature, cloudiness, sunshine and precipitation were used to characterize weather conditions. They were considered as extrinsic influences, possibly affecting anatomical structures.